Aircraft ground power units are utilized to power aircraft when on the ground. Larger aircraft tend to utilize ground power units which output ac power while smaller aircraft tend to utilize ground power units which output dc power, typically at about 28 volts and in the range of several hundred amps. In ground power units that output dc power, the de power may be developed from a 3-phase ac source such as a static converter or a generator. In either case a transformer/rectifier arrangement may be used to convert the 3-phase ac power to the desired dc output.
Transformer/rectifier configurations for converting 3-phase power to a de output are known, with each configuration including its own set of advantages and disadvantages. One such configuration 10 is illustrated in FIG. 1 which shows a full wave center tap connection 12 with 6 pulse rectification of a 3-phase (A, B, C) input. Notably, the 3 input phases A, B, and C are connected in a STAR (Y) configuration 14 and share a common neutral connection 16, and a single 3-phase transformer 18 defined by one magnetic member can be used for coupling the primary windings 20A, 20B, 20C to the secondary windings 22A, 22B, 22C. Each side of each secondary winding connects to the anode side of a respective diode 24 (d1-d6) to provide the 6 pulse rectification. Notable characteristics of this arrangement are (1) that only one diode 24 conducts at any one time such that each diode conducts for 60 electrical degrees with its peak current equal to the dc load current and (2) the current rating of each transformer secondary winding is 0.408 times the dc load current. Characteristic (1) is undesired when high current systems are implemented because the voltage drop across the diodes can be significant. Characteristic (2) influences the size of the transformer because the higher the current through the secondary windings, the greater the cross-section of the wire needed to form the secondary winding of the transformer.
Accordingly, it would be desirable to provide a transformer/rectifier arrangement with lower diode drops in systems having high dc current output such as in aircraft ground power units.